The Charlie Cube Mark II: 4x4x4 - Update

Update
Build this simpler version instead!

Introduction
When I wrote my post on my charlieplexed LED cube, I never meant to publish build instructions. There are plenty of instructions around and a regular LED cube is much easier to make.

Instead, I wanted to show that it is possible to use charlieplexing for such a cube. And I wanted to share my thoughts on how I got there. So I never published schematics for the cube. Also, it is relatively difficult to draw a 3D electronic structure on a 2D schematic.

But quite a lot of people asked for a schematic. So in the end I just tried my best to draw it in an understandable way. I still think that for someone with some basic knowledge of electronics it is better to try to follow my explanations in the original post. But anyway, here it is.

A Charlieplexed Knight Rider Light

Features

• Low cost and low part count
• Four different flashing patterns, easily modifyable
• Speed control and pattern switching via pot

Introduction
This is nothing special, really. "Knight Rider lights" or "Larson Scanners" seem to be very popular microcontroller projects. I guess they are the next step right after the blinking LED (a.k.a. the "Hello World" program for microcontrollers).

I was recently asked if I could draw a schematic for such a device and in the end I decided to actually build the circuit. That way I could turn it into a blog post and make it available to a wider audience. The other point was that I could get my kids involved in building this.

This version is not exactly a beginner's project, because the charlieplexing is quite complex and turning the schematic into wiring can be a little confusing. So perhaps it is a good project to improve your soldering skills.

The Charlie Cube Mark II: 4x4x4

Project Features

• Minimal hardware
• Wiring more complex than standard led cubes
• LED duty cycle 1/8

Update: There is a schematic and part list available here.
 
WARNING: Do not build this cube unless you know what you are doing! It uses minimal hardware but is difficult to understand.

There is a new design which is much easier to build with a very low part count.

Introduction

When I had finished my first charlieplexed LED cube (3x3x3) I wondered whether my next project should be a 4x4x4 cube. But at the time I thought it wasn't worth the effort. After all, I had just shown that a charlieplexed cube is possible and that it can be done with reasonable effort.

The 4x4x4 would of course have 64 LEDs, which would mean quite a lot of soldering. And since I would definitely want to use bright wide-angle LEDs, it wouldn't come cheap.

But the idea never really went away and when I found a good offer for a set of 100 suitable blue LEDs I simply couldn't resist.

The Charlie Cube

Project Features

• 27 LEDs in a 3x3x3 configuration
• Controller is a AVR tiny13 with 1 kByte of program memory
  
• Programmed in C

Introduction

The idea is not new. You can find loads and loads of LED cubes on the net. Some are small, some are insanely large and some even use RGB LEDs. And I must say I like them all. One LED-cube caught my eye because it mentions that it uses charlieplexing to control the LEDs. Its size is 5x4x4. But the instructable also says that with the 14 ports used it could have controlled 182 LEDs instead of the 80 it actually uses.

This got me thinking. How would you go about if you wanted to make a charlieplexed LED cube with efficient use of the available ports? Basically, with charlieplexing you get a multiplexed 2D matrix. How do you fit that into a 3D cube? (For the rest of this post I assume that you know what charlieplexing is.)

The Nano POV

The Micro POV was about making a really small POV display. I wanted it to be as small as I possibly could make it. And it is small. But when I wrote my post about it, a thought struck me: It can be even smaller. I had used a AVR tiny24 controller, which only has 14 pins. But I could also have used a tiny25, which only has 8 pins (including VCC, GND and reset) and still could control 8 LEDs. How is that possible? Simple: By combining the current saving technique from the Micro POV with the LED multiplexing technique of the matrix display I made. To operate the Micro POV I had used a scheme were always only one LED gets activated at a time. This makes the device perfectly suitable for using charlieplexing. And since I wanted to control 8 LEDs I needed only four I/O ports to do this. This was the birth of the Nano POV.

Musings on Charlieplexing

Some time ago I stumbled over an article about charlieplexing on hackaday.com. Charlieplexing is basically a method to control n * (n-1) LEDs using only n I/O ports of a microcontroller. Say you have 5 I/O ports, then you can control 5 x 4 = 20 LEDs independently! Find more details in Wikipedia. I was fascinated, because I had never thought it was possible to control so many LEDs with so little hardware.

But it seems that charlieplexing comes with a few drawbacks. While this is certainly true, some of these drawbacks are in my opinion over-emphasised, especially when compared to "conventional" LED multiplexing. So I set out to explore the issue, just for the fun of it.